Summer Research Program for Science Teachers

Barbara Lillien

South Shore High School, Brooklyn

2002

 

Identifying Food Nutrients

 

Purpose:    You have just started a job as a food-quality tester.  Your task will be to develop a kit to test foods for sugar, starch, protein and lipids.  The test kit will be used by dietitians who will analyze foods to create nutritional menus for hospital patients.  Your first assignment is to demonstrate proficiency using standard tests for nutrients in foods.

Background:    Substances or compounds that supply your body with energy and the building blocks of macro-molecules are called nutrients.  The food you eat contains nutrition important to your body.   Sugars and starches make up a group of organic compounds called Carbohydrates, which are important in supplying your body with energy.  Some starches provide your body with indigestible fiber, or roughage, which aids digestion.  Organic compounds called proteins are important for growth and repair. Lipids are organic compounds that can supply as much as four times the amount of energy as carbohydrates or proteins.

You can perform qualitative tests to identify the presence of organic compounds in food using Indicators, chemical substances that react in a certain way when a particular substance is present.  Benedict's solution is used to identify the presence of reducing sugars, such as glucose. Lugo's iodine solution is used to identify the presence of starch. Biuret solution is used to identify the presence of protein. Sudan III is used to identify the presence of lipids. A standard is a positive test for a known substance.  Unknown substances can be tested and compared with the standard for positive identification of the substance.

Procedure:

  1. Put on safety goggles and a lab apron

  2. Perform the Benedict's test, select three clean test tubes.  With a wax pencil, label the tops of the test tubes "1" "2" "3"

    3. Add 10 drops of Benedict's solution to each test tube. Heat the test tubes in a hot water bath with a temperature rage of 40-50 degrees celsius for five minutes

    4. To perform the Lugol's iodine test, select three clean test tubes. With a wax pencil, label the tops of the test tubes "1" "2" "3"

    5. Add 2 drops of Lugol's iodine solution to each test tube.

    6. To perform the Biuret test, select two clean test tubes. With a wax pencil, label the tops of the test tubes "1" "2"

    7. Add 3 drops of Buiret solution to each test tube.

    8. To perform the Sudan III test, select two clean test tubes. With a wax pencil, label the tops of the test tubes "1" "2"

    9. Add 3 drops of Sudan III to each test tube.

    10. Dispose of your materials according to the directions from teacher

    11. Clean up your work area and wash your hands before leaving the lab.

    12. What are the controls in this lab?

    13. Which indicator detects the presence of glucose? ___________ starch? ____________ protein? __________ Lipid? ___________

    14. Describe the color change of the indicators in the presence of glucose, starch, protein, lipids.

    15. Which test tubes contain standards that you could use for comparing tests on unknown substances?

    16. You are asked to analyze and compare a food substance with standards for organic compounds. You observe a positive response with Lugol's iodine solution and Biuret solution.  What can you conclude about this food?

Extensions:

Teaching Standards:

Standards A, B, D, E & F

 

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